Filter systems, or filter assemblies, have for example been employed in a variety of applications including hydraulic systems, fuel systems and engine lubrication systems. Application of filter systems for filtering gaseous media are also known. Such assemblies for example use replaceable or exchangeable filter elements that can be installed on a filter head for filtering fluid flowing from an inlet to an outlet port in the filter head while passing through the filtration medium of the filter element. The filter element typically is contained within a filter housing such as a can that can be attached to and be detached from the filter head by means of a rotational connection means such as thread or the like.
Often filter systems are provided with a so-called core element, which may be in the form of a perforated tube which is for example arranged along an inner surface of the filtration medium of the filter element. The core element provides mechanical support to the filtration medium, which normally has a limited structural strength. Hence, a core element provides support to prevent the filtration medium from deforming under the pressure difference that exists across it.
In a so-called spin-on filter, the can, and the filter element are formed as one integral unit, which unit is—when replacing the filter element—removed and discarded as one unit. An integral unit is according to the present application to be understood as a unit which can essentially only be divided into its individual components or elements by destroying the connective parts of the unit.
In other configurations, only the filter element is replaced and the core element and/or the filter housing is reused.
In these kinds of configurations, the filter element, on the one hand, and the core element and/or the filter housing on the other hand form two separate structural units. The invention especially relates to these kinds of configurations, wherein the filter element on the one hand and the core element on the other hand, form two separate structural units. Alternatively, the filter element on the one hand and the core element plus the filter housing on the other hand, form two separate structural units. In the latter alternative case to which the present invention also relates, the core element will be fitted to the filter housing. According to the invention “two separate structural units” means two units which can be assembled together as well as be disassembled from each other whilst maintaining the structural integrity of each of said separate units.
During use the filter element may become clogged to the point that is causes a problem in the system, such as inadequate flow to components downstream of the filter, excessive pressure upstream of the filter element, and/or damage to the filter element allowing the accumulated contaminants to flow to components downstream of the filter element. Normally this is avoided by scheduled replacement of the filter element, or when the system indicates that replacement is required. It is thus necessary to replace the filter element from time to time.
Filter elements commonly have a wall of a filtration medium and an end cap, or end part, with an inlet (or outlet) which can be sealed to the head part of the housing to provide a flow path for a fluid stream to be supplied to the interior or space (or to be extracted from the space) within the filter element. The inlet (or outlet) is provided by a port or passage on the end part of the filter element. The port may e.g. have an O-ring seal on its external surface which is received in a bore within the housing, in which it is compressed to form a seal. Often, such a filtration medium has a cylindrical shape. The fluid to be filtered enters the filter assembly via the inlet, the inlet being arranged in such manner that the fluid can distribute along the outer surface of the filtration medium. The fluid is then forced through the filtration medium whereby contaminants (material) in the fluid remain captured in the filter member and the filtered fluid is forced to an outlet of the filter assembly. As an alternative, the flow may be in opposite direction; the contaminated fluid entering the filter element axially and then being forced through the filtration medium thereby flowing substantially radially outward.
Filter assemblies as described can e.g. be applied to filter oil of a lubrication system or an hydraulic system of e.g. a crane. In order to maintain the fluid flowing through the system (i.e. comprising tubing and a filter assembly), a pump is required. This is due to the fact that both the tubing and the filter assembly represent a resistance for the fluid flow. In general, the pump can be driven by an electrical motor or a combustion engine such as diesel engine for example.
In order to gain access to the filter element when it has to be replaced (exchanged), the head and body parts of the housing can be separated. When the filter element is replaced, also any end cap assemblies or end parts attached to it are replaced with it. Many of such end cap assemblies are provided with a so-called bypass flow valve assembly. Such a valve assembly is provided to allow the fluid to be filtered to bypass the filtration medium in case that the pressure difference over the filtration medium has increased beyond allowable limits. Such an occasion exists for example when the filter member has become clogged or needs replacement, but has not yet been replaced. Also other instances in which the pressure in the fluid system increases beyond allowable limits are conceivable. In such cases the bypass flow valve opens and a bypass flow is established. When such a filter element is replaced, also the bypass flow valve assembly provided in it is replaced. This is also true for the above-mentioned spin-on filters of course.
On the one hand this produces additional waste and on the other hand a relatively expensive assembly is discarded when a filter element is replaced.
It is also known to arrange a bypass valve in the head portion. In general this is done by providing a bore connecting the inlet of the head to the outlet of the head, wherein the bypass valve is arranged in the bore to open in case a predefined pressure is exceeded.